No one can hear me on my iPhone SE (2020) during calls

You should absolutely install the current iOS version (iOS 26.5) unless you lack the free storage space to do so (6GB must be free at all times - Settings > General > iPhone Storage).

Your battery needs replacement as 74% capacity is unacceptable.

Apple Service and Repair for iPhone Battery - Apple Support

Mphone555 wrote:

No one can hear me when I call them. I have a 2020 iPhone SE.

I’m on 18.7.1. I don’t want to install 26.5 in case it makes my phone not work. Let me know if this is not the case. I can’t get a new phone right now.

Is being behind on software the most likely cause? Shouldn’t calls still work in 18.7.1?

My battery is 74% capacity.

Voice memos record clearly. Apple diagnostic said there are no hardware issues.

People can only hear me if I tap the mic or yell (even then they can barely hear me).

I’ve already restarted the phone, reset network settings, toggled voice isolation off.

Your battery is SEVERELY depleted and when batteries are as severely depleted, things don't work optimally. Even worse things can happen, such as the battery swelling, which could completely destroy the phone. You say you can't afford a new phone. The one sure way to ensure you absolutely have to buy one is to ignore replacing the battery. You can schedule this here --> Apple Service and Repair for iPhone Battery - Apple Support