This is a very weird case.
Are you sure there is nothing fishy with your iPhone?
I assume this is a vanilla device (not jailbroken). Otherwise it would make perfect sense.
Which iPhone model and which version of iOS are you using?
Also, I would like to echo that Jaxx is not a custodial wallet. You hold the private keys.
And it makes it even more fishy if you enabled PIN within Jaxx.
Perhaps there is some sort of keylogger installed on your phone but this is quite impossible on a vanilla iPhone due to sandboxing.
In any case, you should wipe your phone to factory defaults and set it up from scratch.
And there is a very high possibility that your seed phrase has been compromised. Never use the seed phrase that you use in Jaxx ever again. Also consider all the private keys within Jaxx compromised so don’t reuse any of them in the future. Start from scratch with a new seed and new addresses.
Please make sure you do not store your seed phrase and private keys online. They will be stolen.
Good luck!