I think they could censor victories and raise losses or fabricated stories, sow doubt at a minimum. Make dead american soldiers trend. Whether we like it or not, most teens get news from tiktok. At a maximum they could brick 150 million phones, use them to ddos, use them to hack/disrupt, etc. steal bank information that is also on your phone. In a war these things would not be off limits. If I were in their shoes that's what I'd do.