Space better. That's all I can really say about this. If you put up your PSI Magnet, then Falco could just fly at you with his Phantasm. I'm not sure how much lag is in that attack after it's done, though, so that might not be as useful for him. When his Lasers hit your PSI Magnet, you can lag cancel out of it. In other words, you can jump out, roll, attack or spot dodge out of your PSI Magnet when absorb-able projectile hits your PSIM.
I think you'd be better off taking the hit from a Phantasm than getting Chain grabbed. You can either duck under Falco's Lasers, use your PSI Magnet until Falco gets close with his Lasers and lag cancel your PSI Magnet or something you haven't already tried. If you don't want to get grabbed, you'll have to space yourself better. Try to retreat your aerial attacks. After you get up to at least 40%, the CG doesn't work.