It's no guarantee he'll get much time off after phase 1 training. He will PROBABLY just get the weekend, unless he keeps getting back-classed until summer holidays. During phase 1 training, he should have to stay behind for the first weekend (unless it's changed) and afterwards he'll be entitled to go every weekend. Unless he is duty weekend and then he'll be expected to work.
I went to HMS Collingwood when I used to be in the navy for training so if any questions, drop a message.