Depends on your phone I guess.

First, you should only use white light. So you may need to turn off your burple lights and turn on some real lights.

Make sure you clean you lens, it really matters.

My phone has different picture modes. One of them is selective focus. This allows you to touch the screen to focus on that spot.

Also some phones offer post processing of images. This can help with sharpness and contrass.

If using your phone you should use a tripod and pro mode if you have one.
And natural light of course

First turn off that purple light and use a while light for photos posted on the forum...

using the phone can be tricky, but if you set it to snap the pic by voice command and place it so you arent touching it, you can get it just right. (ive been known to stack books, or hang it or anything to not touch it)

the newest iphone has the lidar camera so you could get some amazing images! but the cost... may as well buy a nikon. (which makes me wonder about how lidar gets those little beams down into the plants!)

for focus, try touching the screen where you want the focus, but it only works well if the phone is very stable. it will try to find the "face" and "look" harder at the image (a very simplified way of saying it).

and, yep, white light would be best, but if you dont have a purple light on and it has that look check the camera filters. the phone cameras mostly do well in low light, so just turn on a room light and turn off the purple and that should help. if you think you need more or more directed light, use a different phones flashlight. not perfect, but very usable