Append column to text file with prefix of file names

Question

I have various files which contain only one column and I would like to add a second column which contain as rows the names of the prefix of the files:

Example:

file1_phone.txt looks like:

A
B
C

file2_phone.txt looks like

D
E
F

Output:

file1_phone.txt

A file1
B file1
C file1

file2_phone.txt

D file2
E file2
F file2

I wrote this loop in linux:

for f in *.txt; do
    b="${f%%_phone.txt}"
    awk -v RS='\r\n' 'BEGIN { OFS = " " } {print $0, "$b"}' "${f}"  > "${f}".new
done

However, it seems it will give this output:

Output:

file1_phone.txt looks like

A $b
B $b
C $b

file2_phone.txt looks like

D $b
E $b
F $b