Should I buy a smartphone gimbal or a camera gimbal?

It depends on your camera. If you shoot primarily on a phone, a dedicated phone gimbal like the DJI Osmo Mobile 8 or a budget hohem is far cheaper and more portable. If you shoot on a mirrorless or DSLR body, you need a camera gimbal such as the DJI RS series or a Zhiyun Weebill, which are rated by payload (typically 2kg to 4.5kg) rather than phone clamp size.