Ivy league coaches can speak on the phone with potential recruits anytime during HS, but the recruit must call the coach (typically call is set up by an intermediary, such as HS or club coach).
Coaches and potential recruits can generally begin meeting in person, on or off campus, for most sports between summer before and Sept 1 of Junior year. Official visits can start Sept 1 of junior year.
Recruits can verbally commit anytime during HS (again, there are a few exceptions).
Pre-reads with admissions will generally happen summer before senior year, and into the fall. As pikachu linked to, Ivies can’t give out LLs until Oct 1 of senior year, and after a student has submitted their application. Academic LLs can go out in early rounds as well as RD.