Can't send and receive photos on iPhone [with screenshots]

About 2 weeks ago, I noticed that photos I received on my phone wouldn't appear as an image but as a file, like this:

Every image I receive appears like this, even if it comes from an iMessage app:

However I could usually see the images under 'Photos' in the Conversation details so I wasn't too bothered.

At the beginning of this week, I stopped being able to send photos. Photos I try to send as well as any accompanying text will usually send as a text message instead of iMessage (regardless of whether I was connected to Wifi or cellular data) and show as "Not Delivered." I believe this is only an issue with my iPhone. I've been able to send people photos on my Mac through iMessage.

The interesting thing is sometimes the recipient actually receives the photo/accompanying text as a text message even if my phone tells me it wasn't delivered. For example, in this conversation, I know that the other person received the "Not Delivered" messages, even if they're "Not Delivered" on my phone (1) and don't appear on my Mac (2):

1. iPhone - The image and text were delivered as a text message to the recipient.

2. Mac

Other times they just get blank iMessage texts. Sometimes the photos will appear to send normally from my phone, but the recipient will only receive blank texts. For example, I sent a friend 10 photos that appeared to deliver normally on my phone (3). Looking at the same conversation on my Mac reveals that none of the photos were delivered and they actually just received 10 blank iMessage texts (4):

3. iPhone - These photos were not delivered.

4. Mac - This is what the recipient received instead of photos.

Today, I tried to send someone a meme from my phone. Seeing that they didn't reply, I figured it didn't go through and sent them the same meme from my Mac. The second image did deliver from my Mac, but it appears as a "Not Delivered" file on my phone. The text conversation looks normal on my Mac (5) but not on my iPhone (6) so, again, I figure this is a phone issue and not a problem with my iCloud.

5. Mac

6. iPhone

Photos that others send me have also stopped appearing under the Conversation details on my iPhone. Not being able to send and receive photos to/from family and friends is really frustrating and any help would be so so appreciated. I also recently cleared out my phone's storage, so I know a lack of storage space is not the issue here.