Here’s how it works. Let’s say you send 10k sats as your initial transaction, that will open a channel. The channel will have 7k sats in it once they take the 3k sats to open it. Phoenix will give you a small bump in inbound liquidity. So your channel may be able to accept something like 2k or 3k more sats.

If you now send another 10k sats, you’ll first fill the existing channel and Phoenix will open another channel with the remaining sats.

You’ll end up will one full channel (no more inbound liquidity) and another channel with maybe 5k sats in it.