I've always used a TRS cable plugged into line inputs and never had any trouble. That is like saying you have to have earphones with a mic/remote for them to work properly. Not the case. This is no different than plugging in a normal set of ear/headphones with a TRS connector. The phone knows how to handle it based on the connection it sees. A case on the device that would not allow the plug to seat fully into the jack is much more likely the issue than TRS versus TRRS.An iPhone uses a TRRS jack (4 conductor) to connect a mic and a volume control along with left and right audio. The audio cable you have is a TRS (3 conductor). That causes the phone to try to put some DC, possibly pulsed, onto the ground line. That causes noises in the audio. Buy a proper audio output cable that uses the "Apple connector" for the iPhone, and it'll work OK. Connect it to a line input, not a mic input.
My solution to some of the issues with connection phones and computers to a sound system is this: