如何通过php从这个json代码获取名为body的字段？

I have been trying everything and I just need help. Thanks I need the body and mobileNumber values and I need each set of values separately in cdv format. Example "Hello little cat!" , "6502642742" "I am home" , "6502642742"

I have tried a few things the last was

$son = json_decode($json);
echo $son->sessions[0]->message[0]->body;

{
   "response":null,
 "sessions":[
  {
     "message":[
        {
           "to":null,
           "body":"Hello little cat!",
           },
           "mobileNumber":"6502642742",
        },
        {
           "to":null,
           "body":"I am home",
           },
           "mobileNumber":"6502642742",
        }
     ],
     "session":"26e2fa57-5d42-4678-bda5-6b233d05b754c:257539402",
     "conversation":[
        {
           "lastContactFirstName":"",
           "lastContactLastName":"",
        }
     ]
  }
 ],
"success":true
}