watching

私が電話したとき、彼はテレビを見ていました。 He ＿＿ ＿＿ ★ ＿＿ TV when I called him.

The correct order is 'He was watching TV when I called him.'. The 3rd word (★) is 'watching'.

正しい語順は He was watching TV when I called him. (過去進行形 was + 動詞の -ing) となります。3番目の空白（★）には watching が入ります。