connecting with macbook

The phone will not appear on the Desktop. If you are using Catalina, then the phone should appear in the Finder's sidebar. You can then perform all essential functions from the Finder by first selecting the sidebar entry for your phone. If you wish to use the iTunes store, then open Music on the computer. In the sidebar under Devices you should see your iPhone listed. Click on it to see your music database. Just above the iPhone in the sidebar is the Store. Click on iTunes Store to open your account.

Where do you want it to appear? If you mean Desktop, then it won't appear on the Desktop. If you are running Catalina 10.15.3, then it should appear in the Finder's sidebar under Locations. The phone needs to be connected directly to one of the computer's USB ports using the charging cable that came with the device.

Is your Mac running Catalina 10.15.3? Select About This Mac from the Apple menu. The OS version is displayed in the second line. If this is the version you are running, then please tell me did you upgraded from Mojave or earlier or did you update from an earlier version of Catalina? Also, you can try the following:

A Troubleshooting Procedure that may Fix Problems with macOS El Capitan or Later

You should try each, one at a time, then test to see if the problem is fixed before going on to the next.

    Be sure to backup your files before proceeding if possible.

1. Shutdown the computer, wait 30 seconds, restart the computer.
2. Disconnect all third-party peripherals.
3. Resetting your Mac's PRAM and NVRAM
4. Reset the System Management Controller (SMC)
5. Reset your Startup Disk and Sound preferences, if needed, after resetting the PRAM.
6. Test in safe mode to see if the problem persists, then restart normally.  Use safe mode to isolate issues with your Mac and Playing Safe - what does Safe mode do?
7. Repair the disk by booting from the Recovery HD. Immediately after the chime hold down the Command and R keys until the Utility Menu appears. Choose Disk Utility and click on the Continue button. Select the indented (usually, Macintosh HD) volume entry from the side list.  Click on the First Aid button in the toolbar. Wait for the Done button to appear. Quit Disk Utility and return to the Utility Menu. Restart the computer from the Apple Menu.
8. Repair permissions on the Home folder: Resolve issues caused by changing the permissions of items in your home folder.
9. Create a New User Account Open Users & Groups preferences. Click on the lock icon and enter your Admin password when prompted. On the left under Current User click on the Add [+] button under Login Options. Setup a new Admin user account. Upon completion log out of your current account then log into the new account. If your problems cease, then consider switching to the new account and transferring your files to it - Transferring files from one User Account to another.
10. Download and Install the macOS Catalina 10.15.3 Combo Update.
11. Reinstall OS X by booting from the Recovery HD using the Command and R keys. When the Utility Menu appears select Install OS X then click on the Continue button.
12. Erase and Install OS X Restart the computer. Immediately after the chime hold down the Command and R keys until the Apple logo appears. When the Utility Menu appears:

     1. Select Disk Utility from the Utility Menu and click on the Continue button.

     2. When Disk Utility loads select the drive (out-dented entry) from the Device list.

     3. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.

     4. Set the Format type to APFS (for SSDs only) or Mac OS Extended (Journaled.)

     5. Click on the Apply button, then wait for the Done button to activate and click on it.

     6. Quit Disk Utility and return to the Utility Menu.

     7. Select Install OS X and click on the Continue button.

What iPhone model do you have? I think you need to have an iPhone 7 or later for this to work. Have you tried unplugging and replugging the cable? Also, try using a different port, if you can.