Should I abandon any further higher education knowing that I was dishonest as an undergraduate?
Sounds like you have had some insights to your past behavior, and understand what you did was wrong - that could serve you will in future situations where you might be tempted to game the system. That experience could be a positive rather than a negative.

You escaped any consequences, and I don't think it's productive to think about hypothetical situations where you didn't, especially for something that is at least a few years in the past.

There are lots of good reasons to not enter a PhD program. I don't think you've found one here, but you should think about what goals you would have as a PhD student since a PhD is unlikely to advance your career unless you want to enter academia. You'll need a lot of internal motivation to get it done. Focus on those things rather than dwelling on your past indiscretions.