How do I make a 4-way conference call with iPhone 5?

As you marked your question Solved I doubt you will get any more responses. This is a user-to-user technical support forum. It's unpredictable how long it will take to get an answer. It's partly a matter of how clear your question is, and if anyone sees it who knows the answer.

So, to come back to your question, that depends on your carrier. For example, if it is Verizon you can never make a 4 way conference call; they only support 3 way.

Conference calling lets you talk to more than one person at a time. You can merge up to five calls for a phone conference.

Start a conference call

1. Make a call.
2. Tap Add Call and make another call. The first call is put on hold. If you want, you can talk on the second line privately before merging the calls.
3. Tap Merge Calls. The calls are merged onto one line and everyone can hear each other.
4. Repeat steps two and three to add more calls to the conference.

To	Do this
Drop one call from a conference	Tap Conference and tap next to a call. Then tap End Call.
Talk privately with a call in a conference	Tap Conference and tap Private next to a call. Tap Merge Calls to return the call to the conference.
Add an incoming call to a conference	Tap Hold Call + Answer, then tap Merge Calls.

I hope this helped you.