Getting an unresolved external symbol error whenever run

Question

I'm having this error but I don't know why it's happening, here it is:

Severity Code Description Project File Line Suppression State Error LNK2019 unresolved external symbol "void __cdecl sdds::comPhone(struct sdds::Phone * const,char * const,int)" (?comPhone@sdds@@YAXQEAUPhone@1@QEADH@Z) referenced in function "void __cdecl sdds::phoneDir(char const *,char const *)" (?phoneDir@sdds@@YAXPEBD0@Z) DIY C:\Users\iv4n3\Desktop\Sem 2\OOP244\Workshops\WS01\DIY\Phone.obj

The code is here:

main.cpp

#define _CRT_SECURE_NO_WARNINGS
#include "Phone.h"
using namespace sdds;
int main()
{
   phoneDir("Star Wars", "phones.txt");
   return 0;
}

Phone.cpp

#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <iostream>
#include <iomanip>
#include <string>
#include "cStrTools.h"
#include "Phone.h"
using namespace std;
namespace sdds
{
    
    void phoneDir(const char* str1, const char* str2)
    {
        char flag[30];
        int count = 0;
        Phone phone[MAX_CONTACTS] = { {0} };
        FILE* fp;
        fp = fopen(str2, "r");
        if (!fp)
        {
            cout << str2 << " file not found!" << endl;
        }
        else
        {
            while (fscanf(fp, "%[^\t]\t%s\t%s\t%s\n", phone[count].name, phone[count].area, phone[count].prefix, phone[count].number) != EOF && count < MAX_CONTACTS)
            {
                count++;
            }
            while (!(flag == "!"))
            {
                cout << str1 << " phone direcotry search" << endl;
                cout << "-------------------------------------------------------" << endl;
                cout << "Enter a partial name to search (no spaces) or enter '!' to exit" << endl;
                cin >> flag;
                comPhone(phone, flag, count);
                cin.clear();
            }
        }
        cout << "Thank you for using Star Wars directory.";
    }
    void comPhone(const Phone phone[], const char flag[], int count)
    {
        int i = 0;
        int j = 0;
        char str1[30];
        char str2[30];
        while (j < strLen(str1))
        {
            str1[j] = toLower(flag[j]);
            j++;
        }
        while (i < count)
        {
            j = 0;
            while (j < strLen(str2))
            {
                str1[j] = toLower(flag[j]);
                j++;
            }
            if (strnCmp(str1, str2, strLen(flag)))
            {
                cout << phone[i].name << ": (" << phone[i].area << ") " << phone[i].prefix << "-" << phone[i].number << endl;
            }
            i++;
        }
    }
}

Phone.h

#pragma once
#ifndef _PHONE_H
#define _PHONE_H
#define MAX_CONTACTS 30
namespace sdds
{
    struct Phone
    {
        char name[20];
        char area[10];
        char prefix[10];
        char number[10];
    };

    void phoneDir(const char* str1, const char* str2);

    void comPhone(Phone phone[], char flag[], int count);
}
#endif

cStrTools.cpp

#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <iostream>
#include <iomanip>
#include "cStrTools.h"
namespace sdds 
{
    char toLower(char ch)
    {
        if (ch >= 'A' && ch <= 'Z') ch += ('a' - 'A');
        return ch;
    }

    int strCmp(const char* s1, const char* s2)
    {
        int i;
        for (i = 0; s1[i] && s2[i] && s1[i] == s2[i]; i++);
        return s1[i] - s2[i];
    }

    int strnCmp(const char* s1, const char* s2, int len)
    {
        int i = 0;
        while (i < len - 1 && s1[i] && s2[i] && s1[i] == s2[i]) {
            i++;
        }
        return s1[i] - s2[i];
    }

    void strCpy(char* des, const char* src)
    {
        int i;
        for (i = 0; src[i]; i++) des[i] = src[i];
        des[i] = 0;
    }

    int strLen(const char* str)
    {
        int len;
        for (len = 0; str[len]; len++);
        return len;
    }

    const char* strStr(const char* str, const char* find)
    {
        const char* faddress = nullptr;
        int i, flen = strLen(find), slen = strLen(str);
        for (i = 0; i <= slen - flen && strnCmp(&str[i], find, flen); i++);
        if (i <= slen - flen) faddress = &str[i];
        return faddress;
    }

    int isAlpha(char ch)
    {
        return (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z');
    }

    int isSpace(char ch)
    {
        return ch == ' ' || ch == '\t' || ch == '\n' || ch == '\v' || ch == '\f' || ch == '\r';
    }

    void trim(char word[])
    {
        int i;
        while (word[0] && !isAlpha(word[0])) {
            strCpy(word, word + 1);
        }
        i = strLen(word);
        while (i && !isAlpha(word[i - 1]))
        {
            word[i-- - 1] = 0;
        }
    }

    void toLowerCaseAndCopy(char des[], const char source[])
    {
        int i = 0, j = 0;
        for (; source[i] != 0; i++) {
            des[j++] = toLower(source[i]);
        }
        des[j] = 0;
    }
}

cStrTools.h

#pragma once
#ifndef _CSTRTOOLS_H
#define _CSTRTOOLS_H
namespace sdds
{
    char toLower(char ch);

    int strCmp(const char* s1, const char* s2);

    int strnCmp(const char* s1, const char* s2, int len);

    void strCpy(char* des, const char* src);

    int strLen(const char* str);

    const char* strStr(const char* str, const char* find);

    int isAlpha(char ch);

    const char* strStr(const char* str, const char* find);

    int isAlpha(char ch);

    int isSpace(char ch);

    void trim(char word[]);

    void toLowerCaseAndCopy(char des[], const char source[]);
}
#endif