Phone cameras are small computers that combine many frames to create a sharp image. When something interrupts that process, the result looks blurry even though the lens is fine. The most common interruptions are motion, low light and a dirty lens.
A smudged lens is the easiest to fix and the easiest to miss. Fingerprints and pocket lint scatter light, creating haze, halos and reduced contrast. Cleaning the outer glass with a soft cloth often transforms image quality instantly.
In low light the camera keeps the shutter open longer to gather more light. Any movement during that longer window, either from your hand or from the subject, turns into blur. Resting the phone on a surface or using a higher light source helps more than any setting.
Some cases, stickers or third-party lenses cover part of the camera or the laser focus sensor. The camera app may not report this, but the pictures will look soft or misfocused until the obstruction is removed.