Hello en146,
Thanks for using Apple Support Communities!
We understand you are having issues with your library loading and syncing on your iPhone. We are happy to look in to this with you and provide some guidance.
To start, we would want to make sure that your settings are set properly. If you're attempting to sync your music when connected to cellular data, please go to Settings > Music > Cellular Data. Confirm Cellular Data is turned on, as well as Streaming if you plan on streaming music using cellular data.
We can also test to see if anything changes when you connect your device to Wi-Fi.
If you haven't already, let's also try force restarting the Music app on the iPhone. Take a look at the steps here:
How to force an app to close on your iPhone, iPad, or iPod touch
If the issues continue, we'd like to ask some additional questions to help get a better understanding:
1.) What iOS version is on your device when you check Settings > General > About?
2.) Can you load and play music from the For You, Browse, or Radio tabs in the Music app?
3.) Is Low Power Mode enabled in Settings > Battery?
Best Regards.