Check If only numeric values were entered in input. (jQuery)

There is a built-in function in jQuery to check this (isNumeric), so try the following:

var phone = $("input#phone").val();
    if (phone !== "" && !$.isNumeric(phone)) {
  //Check if phone is numeric
  $("label#phone_error").show(); //Show error
  $("input#phone").focus(); //Focus on field
  return false;
}

You can use jQuery method to check whether a value is numeric or other type.

$.isNumeric()

Example

$.isNumeric("46")

true

$.isNumeric(46)

true

$.isNumeric("dfd")

false

Try this ... it will make sure that the string "phone" only contains digits and will at least contain one digit

if(phone.match(/^\d+$/)) {
    // your code here
}