It's one of the contacts in the phone's list, should appear directly at the top.
As for cars disappearing, one thing I've been checking is the same case in regard to helicopter use. The closer you remain to a vehicle, the better chance it will remain where you left it, this is somewhat normal game logic at work. I ran some distance from a landed helicopter and it remained where I left it, I took a car to a remote weapon pickup I mentioned near the cove of the ocean inlet, two different attempts, one too far away, the car vanished but it's tracks remained so I know it was the same location, the other time, just above the water where I could see it from the bay, it remained there the whole time, but you could turn your back, attempt to get a new vehicle, and even in close proximity the one you had prior will vanish without a trace.
Want to add two more moments where vehicles were absconded by NPCs, one time a woman came running down the sidewalk following a police shootout, and she took off in the police car left in the wake, The officers had either died or vanished. At least two humorous situations I noted in single player, it's been said that if you parked a police car, the police would obviously take it back. I landed a car near the inlet waterways of LS and the car was blocked on all sides from driving off, but not long after getting out on foot, the message came that the police had also impounded THAT vehicle! Simply by magic it seems!