How do you actually select colleges for Ph.D. application If I have to pick 5 to 6 colleges to apply for a Ph.D. program, how do I go about it?
If I find the work that a CS professor at let's say UC Davis to be interesting. How do I actually know if I have a realistic chance of getting in? I cannot reach out to the professor and ask him if he will let me be a Ph.D. student in his lab because he hasn't seen my transcripts, read my LORs, or doesn't know me at all. If I write him an email, in all likelihood, he will just ignore my email.
At the same time, I cannot ask my recommenders if I have a chance of being accepted at UC Davis. Because (a) They don't know what the other recommenders will write in their letter. (b) They might not know exactly, what sort of profile gets admitted at UC Davis. (c) It's been 3.5 years since I graduated with a Master's degree and 6 years since I graduated with a Bachelors. People might not even recognize who I am, let alone write me a letter of recommendation.
Applying to colleges costs money. Also, people who write me a LOR, have to upload their LOR to each place where I am applying to. If I am applying to colleges way out of my league, I will be wasting my time as well as the time of the people who would write me a LOR.
So my question is, how do you find colleges that are in your league.
I spoke with a few professors for informational talks and they helped me find professors doing research of interest.  One professor I spoke with, I mentioned my research interests and she gave me a list of all the professors who do that research and their schools.  That ended up being the list of schools I applied to.  The most important thing for acceptance into a PhD program is a professor who wants to work with you (and ideally willing to fund you).  I would say base where you apply on the professor(s) in a program you'd like to work with based on topic AND personality. Also, when reaching out to professors for informational meetings please do some research on them.  I find it frustrating when I have potential students reach out who clearly haven't done a basic review of my research area. When I was applying I would normally check the website out before writing an email and then read the abtracts of 1-3 papers that interested me before I met with them.