iCloud Photos, as recommended by MichaelB2019, is the easiest way to let all changes you do on the Mac sync to the iPhone. The Photos Library on the Mac and on the iPhone will be always identical.
But you have to plan how to design the Photos Library you want to use with iCloud. The available storage on all synced devices and storage subscription for iCloud will be the bottle neck for your library size.
The iCloud Photos Library should be small enough to fit onto the device with the smallest storage and into your iCloud Storage subscription. If your current library is much larger, make a copy of the library to be used with iCloud and keep there only the favourites and the important albums you want to have on all your devices.
Alternately, if you are having a fast and reliable internet connection wherever you are going, consider to use the "Optimise Storage" feature. With "Optimize Storage" enabled you can have a larger library in iCloud than on your devices. But you will need an internet connection to work with your photos.