It doesn't use a seed phrase. Block holds a backup wallet for you. Therefore, if you lose both your phone and Bitkey, you must contact Block customer support to receive your lost funds. In short, not having a seed makes you completely reliant on Block and doesn't teach anyone anything about independent financial security. It just grants more unneeded convenience. Convenience >>> laziness.
Discussion
If you lose the two other keys, Block holding the third key doesn't help. If you have a Bitkey, anyone attacking you will know that you must have a second key.
Not exactly right. If you lose your phone and hardware you can recover without Block with the cloud backup and trusted contact. Block just helps with the delay and notification, and if they are not available you have the Emergency Kit to do a sovereign recovery