As tanager16 says, it's obvious you're dealing with dim light and cloudy weather. A "serious" photographer is one who's willing to camp out where the wildlife is and wait for good weather and that perfect evening light...
But there's other things you can work on too.
Most cameras (including on phones) allow you to adjust the exposure. Some will even automatically "bracket" the exposure, taking three or more shots so that one is a little over-exposed, one is under-exposed, and one is exactly the way the light sensor thinks is right.
Your first photo, you're shooting up into the sky. Even though the sky is cloudy, it's considerably brighter than your subject (the hawk), and your camera is setting the exposure a little too dark for the bird. You want to increase the exposure a little, maybe half an f-stop's worth.
Second photo, the exposure is fine, but the focus is off. You're focused on the branches in front of the bird. This is extremely common (and extremely frustrating) when photographing birds in trees. It's virtually impossible for autofocus to solve this problem; you need to use manual focus. You know you wanted a big fancy lens anyway...
Third photo: I love this composition, but the photo has a few small problems at full size. It's noisy, soft, and shows some color aberration. Some fixes: use a tripod, so you can use a lower ISO value (with longer exposure) for better color and less noise. Use a larger-diameter lens, so you can get more light with the same short exposure. Use a more expensive lens, to reduce chromatic aberration. All three together would be best.
Fourth photo: this is the opposite situation from the first photo. You want to under-expose this at least half a stop.
Last photo. Exposure is fine. It's got some of the same problems as the third photo, with some of the same fixes. In general it looks like it was taken in dim light and there's not a whole lot you can do to change that, though some post-processing can help a little.
It can be time-consuming and takes some practice, but it's possible to improve exposures and some other problems after the fact, using software like Photoshop or the GIMP. Note that, although it's usually possible to brighten an image that's too dark, it's not possible to recover details from an image that's way too bright.