Placing a call on "Hold" using Softphone app on iPhone iOS 14.3

I'm using the Comcast Business app to answer my business phone.  I came across a problem:  I can't place a call on "Hold".  I came across this problem when speaking to a Comcast customer support specialist who wanted to call me to verify I was the person on the account.  I also could not figure out how to answer the second call while the first was in progress.  

Can you help?