I don't know the exact numbers, but I imagining it is substantial in the short-term.
Also, this motivates China to produce more components domestically, which will permanently sway Chinese companies away from US suppliers, so in the long-term, this could do tens of billions of dollars in damage to the US.
Perhaps the assumption is that ZTE's competitors sourcing similar US components will make up the difference in increased sales when ZTE's business falters.
ZTE order lots of electronic parts from US. The supply chain would suffer. Also the are some small carriers which relies on cheap Chinese Huawei/ZTE phones and cell towers.
Also, this motivates China to produce more components domestically, which will permanently sway Chinese companies away from US suppliers, so in the long-term, this could do tens of billions of dollars in damage to the US.