Seriously, if you are planning to photograph wildlife from a long distance, you'll want something else than a monocular add-on to a smartphone.
You need:
- Ability to use fast shutter speed (1/1000) because wildlife can be... wild, and run/fly fast.
- A decent aperture. Note the aperture number is effectively multiplied by the crop factor, which on smartphones is huge (crop factor, that is).
- If photographing in any conditions other than sunlight, good high ISO performance, meaning the sensor should be far larger than a smartphone sensor.
- Image stabilization could be a bonus as well, but my experience is that fast shutter speeds (1/1000) don't need it. Still, in low light, photographing non-moving or slowly-moving wildlife, image stabilization can be mandatory.
- A long focal length.
- A high-megapixel sensor.
- A good lens, because lens can limit the image quality, and even with a long focal length, you may need to crop the image.
- Good ergonomics on the camera. Aiming a 400mm-equivalent lens isn't easy.
- A display / viewfinder that can be viewed in sunlight.
- Burst mode to take number of pictures within a short time interval.
- Fast autofocus
Let's see what a smartphone has:
- Shutter speed: is this even adjustable? Probably not.
- Aperture: whatever it is, the crop factor means it's effectively too small in size (too large in number).
- Good high ISO performance: no, due to the sensor size
- Image stabilization: yes, but if you use a monocular, it probably means the IS gets confused and doesn't work as it should.
- A long focal length: can you get long enough on a monocular?
- A high-megapixel sensor: modern smartphones may have it, so yes, you can have enough many megapixels.
- A good lens: NO!!!
- Good ergonomics: no, smartphones aren't made for camera use ergonomics
- A display / viewfinder that can be viewed in sunlight: no
- Burst mode: I don't know, may depend on the smartphone, and autofocusing in a burst isn't probably fast enough if at all supported
- Fast autofocus: no, and especially no on a monocular
If you don't have much money to spend on this, you could purchase a cheapish crop sensor DSLR (avoid the cheapest of them all to avoid the ones having slow burst mode) and a cheap crop sensor telezoom. Do expect to spend nearly $1000 for the setup, however. This $1000 is what photographers consider "cheap", some laypersons could consider it expensive. I used to photograph wildlife with Canon 2000D and 55-250mm. The lens quality may be ok but not stellar. The camera has too small buffer for the burst mode. I missed a huge number of potential shots due to the small buffer for the burst.
A better setup would be a full frame DSLR / mirrorless and a professional telezoom. For example, I currently have EOS RP and a second-hand 100-400mm L (the first version of the lens) for $2000 total (purchasing the second version of the lens for new would have cost with the camera $3500 total). It's much better than the first setup, but still some could argue the burst of the EOS RP isn't fast enough.