Please don’t give up. You will get to confession some time
As regards to your phone, my mobile phone, I can delete all traces of any calls or texts that I make so you probably can. If you get into the habit of it then parent may well suspect but that their business and nothing for you to worry about. It isn’t like you are planning something illegal.
But failing that, go to a phone box and ring from there and as you are explain to the priest your situation so he knows not to say anything to your parents if he sees them. By the way you do know confession can be heard anywhere so if getting to church is hard then the priest and you can find a mutual place where you can have confession in privacy.
Or will one of your friends let you use their mobile phone to ring the priest? It upto you whether you tell the friend the whole truth etc. Make sure though that when you are in contact with the priest that he is aware of the total privacy that you need because your parent dissapprove. Priests usually are as obliging as they can be. The severity or not of your sins doesn’t matter because God doesn’t judge them like that and the priest will work with you hopefully so that you can get there and not be given away, Our priest is totally confidential so I can trust him.
Please keep working at it and you will make it to confession this year. Do you have a pastoral care worker at school who you could go and approach, tell them the whole thing and ask if they would set up confession for you with a priest even on a regular basis making it clear about your parents? Or just keep turning up to that mass time and one day that priest may well be there. Please don’t give up because it is important to you.
Peace be with you