Can Phoenix wallet steal my funds? Phoenix wallet is a great UX Lightning Wallet, and they're able to deliver that UX by making a few different tradeoffs. None of those tradeoffs involve them owning your private key, but in their 2019 blogpost they write:

Phoenix only connects to ACINQ nodes. This allows us to modify/enrich the Lightning protocol at the immediate peer level, while staying 100% LN compliant at the network level.

Since I'm only connecting to ACINQ nodes, could ACINQ (the corporation) theoretically use their nodes to say I'm &quot;cheating&quot;, thereby forfeiting my LN BTC?
Thanks!
If you can verify that Phoenix is running the code that you expect - the open source eclair implementation of the Lightning Network and Phoenix wallet - then they will not be able to use their node to &quot;say that you're cheating&quot;. This is because they do not have signatures for your unique commitment transaction, so there's no chance that they can broadcast your commitment and then claim the penalty for themselves.
More generally, mobile wallets that depend on their channel peer for blocks could theoretically cheat their peers by broadcasting old state and then withholding blocks until the time that your node has to claim the penalty output. Phoenix has an option to connect to your own electrum server, which would protect you against this (unlikely) attack if you chose to enable it.