Joining a meeting works on phone but not computer

There are a number of possibilities based on the info given. It may have been the host. One possibility is that you joined while the waiting room was on and the host disabled the waiting room but did not admit you thinking that disabling the waiting room would admit everyone. When in fact disabling the waiting room only admits those who join after it was disabled. Anyone in the waiting room (which they can see on the participant list) must be admitted by the host or co-host. If you leave the meeting and rejoin and get in this is the likely scenario. If you join with another device at a later time and get in that would be the same.