Forgetfulness
As a man left the cafe, Maria saw that his phone was still on the table. What could she do?Bravo! Writing in another language is hard work.
The Forgotten Telephone
As the man left the cafe, Maria saw /that his phone was still on the table/that he had left his phone on the table. What could she do?Notes -
a man left the cafe / the man left the cafe
With different wording, "a man" would be required
A man entered the cafe. He had a coffee. As the man left, Maria saw ...
In this story, starting with "the man" provides dramatic focus and is natural. A teacher for beginning students would suggest "a man" to reinforce basic grammar whereas a teacher for advanced students would suggest both "a man" and "the man" and then explain the difference.
As the man left the cafe, Maria saw ...
Action verbs
his phone was still on the table
he had left his phone on the table (action verbs are preferred)