External Hard Drive for MacOS Sierra 10.12.6

Thank you for asking. Here are some helpful thoughts.

• The disk typically needs to be formatted the same format as your HD. Use Disk Utility to do the reformatting, not any utility app provided by the disk vendor. They cause problems and should be deleted.
• The external drive should be large enough to accept 3 times the data on your HD, not including the OS. (It is not backed up.)
• The backup disk should be exclusively dedicated to backups only.
• It doesn't matter if you use a mechanical drive or an SSD for backups. Mechanical drives will cost less.
• Most any brand will do the job. I personally like and use LaCie drives.

Here are some further thoughts.

• I would definitely use a dedicated drive for the backups and a separate disk for booting from an external drive.
• I agree that the drive used for booting should be an SSD. They are much faster than mechanical drives, but they do cost more to purchase.
• You will need to download and install an operating system (OS) on the startup external drive and then open System Settings to set it as the startup disk if that is what you want.
• If you wish, your iPhone can be backed up to your iCloud account. iCloud is not for backing up a Mac computer, however. Only iPhones and iPads.

OK, You're grasping it pretty god my friend.

I'd recommend an external SSD if you want to boot from it...

https://eshop.macsales.com/shop/owc-envoy-pro-sx

https://eshop.macsales.com/shop/owc-envoy-pro-fx

If just for Time Machine use a USB HDD would work...

https://eshop.macsales.com/shop/owc-mercury-elite-pro

Does the “disk” mean the External HD?

Yes, And Correct.

Would 2TB be large enough or do I need more?

I would think so.

Since it is my laptop and I don’t have a home Desktop, should I get a portable HD?

Likely so.

Can I back my IPhone 11 on the same HD?

Will the HD recognized duplicates since my Laptop and IPhone sync together ?

Can I erase photos from my iPhone and Computer , after I back them up to free up space ?

Yes if booting from the external drive.

Syncing should work.

No, you need to transfer everything to the External drive, I recommend Carbon Copy Cloner seems to accomplish it...

http://www.bombich.com/software/ccc.html

I know eventually I’ll have to replace my computer and IPhone . Do I need to worry about my HD being obsolete ?

You shouldn't but who knows the future for certain?

I just don’t want to lose pictures of my parents or voice messages from my mom that I have saved for 5 years .

I'm going tom recommend you get both, an External SSD to boot from + an external Drive or SSD to backup to, since you have important irreplaceable data.:)

Just holler If I didn't cover anything.

Make sure it is NOT formatted APFS, Sierra cannot understand APFS & needs MacOS Exteded Journaled, GUID partition scheme.

Fantastic to hear my friend, do let us know how i's going.:)