Apple iPhone 6 ghost touch fix?

If it only happens when plugged in it is a bad cable. If it happens all the time it is a bad screen digitizer. Here is the repair pricing from Apple—>iPhone Screen Repair & Replacement - Official Apple Support. You can find lower prices from some independent repairers, but they will not use Apple-designed replacement screens, so you will lose features like True Tone and, if they aren’t careful or if they replace the HOME button, Touch ID will no longer work.

If it happens only when plugged in replace the cable.

If it happens at other times in needs a new screen assembly.

Take it to Apple for an assessment. Could be a new screen, or new phone which considering the age would be more cost effective

https://support.apple.com/repair

I still would not send that kind of money on an obsolescent phone.

iPhone Screen Repair & Replacement - Official Apple Support

Apply Lawrence Finch's test first.

"...It's my second time in a row with this problem...."

Twice would be statistically unlikely.

Either very bad luck, or the way you treat the phone??

I still think $400 for a new iphone SE is better value than $200 for a new screen on an old boiler phone.

I'm pretty sure this issue is quite common as my friend and I both have it and there is a lot of information and articles online about this issue. As far as I've read it's a design issue more often than a user issue. Since it's so expensive to repair and doesn't update anymore I'd agree its not worth repairing.