I'm an old man with 3 kids so I know s thing or 2...
Venetorem had it right, better to own up to it than to be in trouble for multiple problems all at once. Personally I forgive my kids for more than they expect if they save me the time of playing detective. Plus they may not appreciate you putting yourself at risk by being out of touch without their knowledge.
If you want to try to soften the blow, tell them you have something important you need to talk with them about and then give them time to worry about all the horrible things you may have done like burglary, arson, unwanted pregnancy, etc. then break the news that it's a lost phone.
It wouldn't hurt to offer to be extra helpful around the house and work off your debt.
Good luck.