So i want to join the army at 17... Need someone that has done this before.?

If you are 17 then you will enlist under adult entry, this means you will go to ITC Catterick. where you will complete the combat infantryman's course that lasts 26 weeks. There is no such thing as Phase 1 & 2 for infantry. If you join a corp then you do 14 weeks CMS (R) (Common Military syllabus (Recruits)) then you do your phase 2 trade training. To be honest your best bet is actually the careers office they can answer all your questions.