How to append int to string in PHP? -

I have a clicklet integration in my shop. I need to include my country code (45) in front of the phone number which sends to the API.

I have this code that pulls the phone number from the sequence. How do I enter 45 in front of the phone without spaces?

  $ from $ commandData-> phone;   
 I am thinking like this:  
  $ from $ 45 = OrderData-> phone;   
 But I do not have enough information about this work.   
 
  $ code = $ 45 = $ OrderData-> phone;   
 Should do this.