Aha... the daemon has some docs in help: ./phoenixd --help

Liquidity Options:
--auto-liquidity=(off|2m|5m|10m) Amount automatically requested when inbound liquidity is needed (default: 2m)
--max-mining-fee=<int> Max mining fee for on-chain operations, in satoshis (default: 1% of auto-liquidity amount)
--max-fee-credit=(off|50k|100k) Max fee credit, if reached payments will be rejected (default: 100k)

Options:
--chain=(mainnet|testnet) Bitcoin chain to use (default: mainnet)
--mempool-space-url=<value> Custom mempool.space instance
--http-bind-ip=<text> Bind ip for the http api (default: 127.0.0.1)
--http-bind-port=<int> Bind port for the http api (default: 9740)
--http-password=<text> Password for the http api (full access)
--http-password-limited-access=<text> Password for the http api (limited access)
--webhook=<value> Webhook http endpoint for push notifications (alternative to websocket)
--webhook-secret=<text> Secret used to authenticate webhook calls
--silent, --verbose Verbosity level (default: prints high-level info to the console)
-v, --version Show the version and exit
-h, --help Show this message and exit

I guess I should have started with testnet, or maybe setting --auto-liquidity way lower when testing would be smart, but I'm not gonna touch that right now!