Calls underwater but not on facetime or speaker

Hi,

I have a very interesting issue which I can’t figure out, I have an iphone SE first edition not the new one.

when I make a phone call it sounds like I am under water but this is where it becomes interesting. Few points below:

• Normal phone call with the cellphone to to my hear - sounds underwater
• Normal phone call but on speaker - works fine
• facetime call on spreaker or with the cellphone on my hear - works fine and whatsapp the same
• recording an audio on WhatsApp or using the audio record app from apple also - works fine

I cannot understand whats is wrong since facetime and WhatsApp call with the phone on my hear work fine but not on a normal call ?!

Any idea what could be wrong?

Thanks