The most likely cause is an internal camera problem, not dirt on the outside of the lens. Based on the sample description, the spots could be either:

• dust very close to or on the sensor/optical stack, which can create dark marks in every image, or
• sensor damage/failure, especially if the spots look pixelated or appear in clusters rather than as soft blurry blobs.

Typical dust usually appears as softer, blurry spots, while sharply shaped or pixel-like black marks can point to sensor damage. One community answer also notes this kind of clustered damage can happen from laser exposure or impact damage.

Because this is inside a phone camera module, it is generally not user-serviceable. The practical fix is to have the phone professionally serviced or the camera module replaced. If the number of spots is increasing, that further suggests an internal hardware issue rather than something you can clean externally.