Yeah, definitely not a co-lead. Mar-Vell & Fury should be more prominent than Phil. I'd say about Thor 1 levels would suffice. Or a little less. Just...there, but the relationship should probably be more focused on Nick & Phil rather than Carol & Phil. Like show Phil coming into his own as an agent and proving himself, show why he's Fury's trusted go-to in the later films. Frankly, while he probably will interact with Carol, I'd actually be just as fine if he didn't. I kinda love the idea of Carol being this huge secret ace-up-Fury's-sleeve he doesn't fill anyone else in on, y'know? Get into the "his secrets have secrets!" stuff. Phil can kind of help him out, but not necessarily be directly in on the significance of what's going on, more a peripheral player that Nick senses is a good honest man and who he's starting to trust, slowly bringing him in on all the crazy cosmic/superpowered stuff but only in a broad general sense rather than directly "hey, meet Carol, she can fly & punch holes through asteroids!"