Gatling: JSON Feeder Data is not getting picked up by the session

Question

Likely I am using the wrong syntax. Here is the code:

  val jsonFeeder = jsonFile("data.json").random

  val request: ChainBuilder = {
    feed(jsonFeeder).exec(
      grpc("RequestType")
        .rpc(API.getSearchMethod)
          .payload(SearchRequest.newBuilder()
            .setSearchCriteria(SearchCriteria.newBuilder()
              .setUserData(UserDataCriteria.newBuilder().setPhone("${user_phone_number}")
                .build())
            .build())
          .build())
        .extract(_.getList.some)(_ exists)
      .extract(_.getCount.some)(_ saveAs "Count")
    )
  }
  scenario("search for owner personal info phone number").exec(request).exec { session =>
    println(session("user_phone_number").as[String])
    session
  }

The issue is, the setPhone is not getting the actual user_phone_number value, but the second exec with the session is finding it.

Why is it not working for setPhone?

EDIT: I've realized I am not use Gatling EL correctly, but still the question remains, how can I use Gatling EL in my own function? How can I get this jsonFeeder data to set the phone value?