Hi JMEJ, I can understand the option of making a conference call on your iPhone 5s and I like to help youn with this inquiry. The function you wish to do is also known as 3 way calling and it normally available on most devices. Do you have any issue with 3 way calling? Here's a link for the steps and information on 3 way calling http://tiny.cc/ogtz3x and if you have any issues with this function, share more information so we can assist further.
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