I am using Mojave. I find that the information on my MacBook Pro and my Iphone are not syncing. How can I fix this problem?

Try going to iCloud.com using a computer browser to see if the items are there and whether they are from the device or the computer. That should show whether the device or the computer isn't syncing. If the computer, try going to System Preferences/iCloud (Apple ID if you are using Catalina) and stop syncing. Wait a couple of minutes, then recheck syncing. If the device, go to Settings/Your Name/iCloud and do the above. As a last resort, you can also try signing out of iCloud and then sign in again.