How to deal with Echo knight fighters?

I have a upcoming campaign I am running and 1 of the players is going with a echo Knight fighter. I think it looks like a really fun class and am happy for them to play it.

My question is how do you as a DM deal with the Echo in combat? the description of the echo "echo is a magical, translucent, gray image of you" makes it clear that the echo stands out from the PC.

Do you still attack it as if its a combatant? it can deal damage can cause things like flanking etc or do you ignore it knowing that attacking the actual PC makes more sense.

The 2nd option seems shit as it will ignore the players Subclass main gimmick, but also focusing attacks on a echo seems silly as its just a phantom....

Appreciate any suggestions. I want everyone to have fun but I still want a challenge in combat and the fighter is the main tank of the party.