Ah, that is a bit unfortunate.
I think now you basically have to attack. Other options:
1. Defend in city. Actually worse, city raider promos, no culture. I don’t think one unpromoted, unfortified archer will help
2. Move army out. An option, but I don’t think you can afford to lose Tokyo (and I’m sure your horses would be pillaged soon after).
Glass half full version - well it’s much more fun to take out this stack on the flatland than fortified in a hill city!
I think this basically means your target is Alex too, get a new army and go after him! Hopefully he’ll focus on phalanxes from now on!