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.
Congratulations on your Ph.D. Don't stress over the minor errors.
A Ph.D. is a mark that you are capable of absorbing the state of the art in a certain (sub)field and contributing novel knowledge. Your dissertation documents this, as well as shows you are capable of communicating about it. It seems you ably did all this.
A Ph.D. dissertation is not meant to be perfection and rarely is. As you progress in your career, academic or otherwise, your future work will invariably eclipse it. It is a rite of passage, not your lifetime supreme achievement.
Some Ph.D.'s eventually realize their dissertation contained substantive errors. Not typos or suboptimally written phrases, but methodological or logic errors significantly affecting the validity of the results. In some fields where there are different schools of thought, successful Ph.D. dissertations may well become controversial, and their flaws more apparent over time. This is all part of the academic process.
Even those of us spared of the above will generally wince at something when rereading our dissertation years later. It may not be a grammar error or maladroit sentence, but very often some of what we wrote seems -- with the benefit of hindsight -- very naive, or at least very earnest and self-important. That's more wince-worthy than a typo or weird sentence!
The Ph.D. and the dissertation in particular are part of the learning curve. If you continue down an academic career path, what took you several years the first time around will soon take you several months, and be better. That's normal.