Use a running armband
Use a running belt or waist pack
Carry it in a shorts pocket with a secure zipper
Use a handheld phone strap
Use a hydration vest with a phone pocket
Use compression shorts or leggings with a phone pocket
Place it in a slim crossbody running bag
Choose a case with a grip or strap
Keep it snug to prevent bouncing
Use sweat-resistant or waterproof protection