Wait until you have at least a couple million sats in Phoenix and then move it on chain to your cold storage. (Don't keep more in Phoenix than equivalent to an amount of cash that you would keep stashed somewhere in your house though.) This way you keep your cold storage UTXOs large. That will matter in the future. Make sure you write down your seed phrase for Phoenix and keep it in a safe place so that you're able to restore the wallet on a new phone. Lastly, it's probably a good idea to use the request inbound liquidity feature (that's Android only for now) so that you don't end up paying miner fees every time you move funds from strike to Phoenix. There's a 1% service fee to do that (you should request a large amount) and you'll pay a miner fee once to splice that liquidity in, but that's better than paying a miner fee to splice in every time you transfer from strike to Phoenix, especially if on chain fees go higher over the next year which I expect they will.

I recommend coldcard for cold storage, but you can really use any offline device that will generate a seed phrase. Seed signer is cheap and works just fine. You can use that seed phrase years into the future to access you funds on any device.