
That sounds frustrating with your phone case cracking so soon and especially since you need something reliable for outdoor work. It might be happening because the material isn't tough enough for frequent drops or exposure to the elements and like temperature changes or rough handling. Cheap cases often use brittle plastics that don't hold up well over time.
If you're looking for a better alternative without breaking the bank, I'd suggest the SPORTLINK phone case. It's designed to be shockproof and dustproof, which should give your phone solid protection from falls and dirt while you're working outside. That full-body coverage really helps in rugged conditions.
Just make sure it fits your phone model, and it could save you from having to replace cases all the time.