PhD manuscript with grammatical errors and informal phrases
Ok. Let the past be the past. You weren't perfect then, you are better now. Maybe not perfect yet, but neither am I, or anyone. The very fact that you can recognize past errors is a sure sign that you are now better at this than you were as a novice scholar. 

As the comments note, there is little chance the problems will be noticed, or even that they will matter if the are noticed. 

There is a phenomenon among writers that is worth noting. Many people, writers of all kinds, sometimes feel embarrassed by their older work. Even poets. It is a sign of growth, not of failure. 

In Tai Chi we say "One day's practice, one day's progress." 



A couple of additional thoughts. 

It is immensely difficult for most people to proof-read their own writings. You tend to see what you thought you wrote, not what you did write. An external review is a great way to improve any writing. See, for example Ezra Pound and the drafts of The Waste Land. 

Also, you would be in far worse shape if you ignored past errors and insisted, insisted, that they were PERFECT.