I recently switched to iPhone and had the same question. The recommendations on akstrategic.com were super helpful. They reviewed several iOS-compatible apps that sync perfectly with iCloud and let you fax straight from your Files app. I picked one from their list, and it’s been great — no lag, no compatibility issues. If you rely on Apple’s ecosystem, go for one that’s optimized for iOS; their guide clearly shows which apps perform best on iPhones.