Conference call on iPhone

Dear Experts,

I used to be able to make conference call from my iPhone, and all of a sudden I cannot.  I have opened a ticket with my carrier (Verizon) and tried to troubleshoot, but they could not help.  My phone is iPhone X, with iOS version 11.4.1.

Please advise.
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Wesley MillerComputer Network AnalystCommented:
When you call somone and get an answer there should be a "Add Call"  on your Apple Display to Conference another party to the call.
Stacy RichardDirector of Member Experience  Commented:
All parties must have iPhones and iPhones have to be on ios12

while on a call, tap add a call
to dial a contact select a contact from the contact tab
to dial a number, dial a number from the keypad tab then tap call or tap the call icon

tap to merge call
yballanAuthor Commented:
Dear Wes and Stacy, thank you for a quick response.  My problem is, Add Call button is not enabled even after the other party picks up.  I have tested another iPhone where I was able to add calls to another iPhone or regular desk phone.  I also put my SIM card into another iPhone to test, and it worked.  There is something about this particular iPhone that does not let me add a call.
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Stacy RichardDirector of Member Experience  Commented:
Upgrade to iso12 or 12.1.3
Wesley MillerComputer Network AnalystCommented:
If the Upgrade doesn't do it then do this, but first make sure you do a full back up by tether to your computer  using iTunes to back up the iphone.

Then on the iPhone,  Settings , General, On the next screen scroll to the very bottom, Press Reset.
1st Try Reset Network Settings if you still Don't have the "Add Call" then try Reset All Settings.

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yballanAuthor Commented:
Thank you, Wes, that did the trick!
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