The Fairphone 5 is only IP55 rated (dust protected, and water droplet resistant). Most flagship phones are IP68 rated (fully dust sealed, and water submersible). IP68 phones are sealed with a single-use adhesive gasket, and replacing battery requires breaking (and replacing) this seal. If the seal is improperly applied, the phone is no longer protected from dust or water.

There is also a middle ground of IP67 from the Samsung Galaxy S5. I'm personally fine with the Fairphone level (they clearly prioritise easy and frequent disassembly; that's their entire brand) but for someone who wants to be able to submerge it just below the surface and walk through pouring rain for hours, that would be enough