Lost all photos from iPhoto

Open a Finder window, navigate to your pictures folder, and tell us what's listed there. My guess is that you have two libraries. Post a screenshot if you can.

So then I tried upgrading my computer and upgrading iphoto, now it's saying "the iphoto libaray needs to be upgraded to work with this software" but I'm scared to hit anything for fear that it'll erase the pictures from my phone and computer.

That is normal - when you upgrade iPhtoo it usually has to upgrade the library the new version - and since you must always have a good backup and certainly never pdate or upgrade software withot one you are proected against the rare problem because you have a backup

Backup your iPhoto library and upgrade your library

LN

Most Simple Back Up:

Drag the iPhoto Library from your Pictures Folder to another Disk. This will make a copy on that disk.

Slightly more complex: Use an app that will do incremental back ups. This is a very good way to work. The first time you run the back up the app will make a complete copy of the Library. Thereafter it will update the back up with the changes you have made. That makes subsequent back ups much faster. Many of these apps also have scheduling capabilities: So set it up and it will do the back up automatically.

Example of such apps: Chronosync- but there are many others. Search on MacUpdateor the App Store