Ear Speaker not working after water damage/screen repair

Hi,

So my friend at work dropped his iphone 6 in the bath a few weeks back. It still worked, but the ear speaker had stopped working.

In an attempt to fix the issue, he used a "Reviveaphone" kit, which I believe involves putting the phone in an isopropyl solution.

This didn't fix his problem, but only made it worse - the phone now wouldn't power on at all.

He then asked me to look at the phone for him as I've replaced many screens & other parts for people in the past.

I took the phone apart, and gave it a week in a ziplock bag with some silica gel pouches. We discarded the battery and replaced with a new one.

The phone powered back on, but the screen was badly damaged and very dark, and the speaker still didn't work.

I've just replaced the screen and it's fine now, but the speaker is still not working.

Is it worth me replacing the camera/speaker flex cable? Or is it more likely to be a fault on the main board?