During a call the speaker button does not work

Greetings TbirdZ2, 

We understand that the speakerphone option is grayed out when on a phone call. 

We’d like to have you work through the steps in the following article If the microphones on your iPhone aren't working

Next, please also launch the Voice Memos app and attempt to record a memo. Are you able to? This is going to tell us a bit more about the microphones in your iPhone and help us determine if hardware may be an issue. 

Thanks. 

TbirdZ2, 

What happened when you tried to recover a memo in the Voice Memos app? When the display goes blank briefly after you tap the audio button, what happens when it comes back? Does it return to the call and are you then able to tap the audio option again? You mentioned it doesn’t happen with every call, does it seem contact specific? Is there any sort of Bluetooth devices paired with your iPhone at the time?

We’d also like to have you make sure your iPhone is up to date and you can verify whether there are any updates available in Settings > General > Software Update. If there are, be sure to create a backup and then install the update. This article can help with both steps: Update your iPhone, iPad, or iPod touch

Next, we’d like to have you restart your iPhone and test the behavior again. Restart your iPhone

We know intermittent issues can be hard to nail down, these steps are going to help us further isolate the behavior.

TbirdZ2, 

Thank you for these additional observations of the issue. Is the proximity sensor that is near the receiver at the top of your iPhone, where you place it against your ear, covered at all when you’re attempting to place the call on speaker? Since the purpose of the proximity sensor is to turn off the display while on a call so you can’t accidentally press a button on the screen, we want to be sure. 

Do any other buttons cause a similar behavior when you’re on a call such as Mute, Keypad, Contacts? 

Thanks.

TbirdZ2,

In addition to continuing to keep an eye on the behavior, we'd like to have you work with Apple Support. The situation appears to be software related and there's a chance they'll want to work with you some more on the software side of things.

Here's a link to reach out to them: Official Apple Support

Thank you.