How can I check if my speaker is messed up

If you have distorted Sound issue on your iPhone --> If you hear no sound or distorted sound from your iPhone, iPad

If you are not able to hear the other person, click this...>If you can't hear a person on a call or voicemail or if the sound isn't ...

If you only hear through speaker phone mode --> If your iPhone is stuck in headphone mode - Apple Support

If the other person is not able to listen to you then please click this--> If the microphones on your iPhone, iPad, and iPod touch aren't ...

If the above options do not mitigate the issues then Contact your carrier and then Contact Apple Support

Microphone is to provide your voice input to speak.

Speaker is the sound you hear.

Microphone is to input your voice into phone

Speaker is the sound you hear from the phone