Multiple ip address but single outgoing ip

hi;

i have several ip adress, a have added all of them in Network section. when i attach one of the ip address to domain, it work, i can reach domain with that ip address. but when using php command
file_get_contents(“https://wtfismyip.com/text”);
inside of that domain, this command return my main address, not attached ip address. what i am doing wrong ? why my outgoing ip cannot change ?