How do I support my boyfriend?

We're in a long distance relationship. He has a start up and he's very busy with it. Still he calls me twice a day, like when he's driving, he always calls me up. We don't get to talk much.. maybe like for 20-30 mins per day at max. He always keeps telling me about his work.. I really don't understand what to respond. We hardly video call. He's always worried about his work, we all know that start ups can be very stressful.. I wanted to know.. what should I say to him? I mean if u guys were in his place what would u all like to hear from us? What can I do to support him, since I don't live with him , I really don't understand what I can do from calls and texts.
How do I support my boyfriend?
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