Phone number validation in php

In phone number validation mostly php regular expression was used.

Example1  91-9874563210

if(ereg("^[0-9]{2}-[0-9]{10}$", $phone_number)) {
      echo "valid phone number";
}
else {
       echo "invalid phone number";
}

Example2  555-655-7516

if(ereg("^[0-9]{3}-[0-9]{3}-[0-9]{4}$", $phone_number)) {
       echo "valid phonenumber";
}
else {
      echo "invalid phonenumber";
}