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.

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.

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

If it happens only when plugged in replace the cable.

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