I work as a designer, so I often do research and also have to test stuff. I often have my phone in my hand or on in front of me as I use a mirroring program to show my designs directly onto my phone while I'm working on them. This helps me a lot with making designs. When a supervisor tells me 'I like Amazon's checkout, we should do something similar', I need to browse amazon, take notes and screenshots etc.
None of my supervisors have issue with this, but my colleagues always make comments. 'Are you done Facebooking, I have a question' when I am holding my phone. Or 'I doubt Amazon is allowed in the office.'. If they need something from me they will say 'You don't have a lot to do right?'. It even goes so far that if I say I've had a stressful day, they will just reply with 'Filled with online shopping?'.
I'm getting a bit sick of it and I feel like I'm losing respect of people. I have explained many times it is work related, but they are not having it. How can I explain it to them without sounding like I'm making fake excuses?