Best way to put music on Iphone?

My computer barely has any space left it only has a 34gb hard drive and I really want new music on my iphone. Any ideas?

Buy a USB HDD and offload all the stuff that doesn't need to be on your system drive.

Or even upgrade your system drive, if you have an older system. If you have a newer SSD only system. Get the USB HDD for your long term data such as music files.