It's a fair point.
Yet, I think if you take into account these costs, you are probably gonna save sats using Phoenix. If you run your own node:
  • You have to open the channels yourself. That has a cost. Plus, force closures can cost you a lot of sats.
  • Acinq's node is one of the best connected nodes in the network. That mains you will probably safe on fees from other hopes in your routes.
I guess it probably depends on how your usage looks like. If you do thousands of transactions, I guess eventually managing your own node will save you sats.