You should always leave five or ten minutes at the end of a phone screening for the interviewee to ask you questions. Good candidates will be prepared with questions about your company and will want to fill in any gaps in their understanding of the role.
If a candidate has absolutely no questions for you, that can be a red flag. Most should have done at least a few minutes research on your company and what you do; the questions interviewees ask are a good way to judge their preparedness and enthusiasm about the position.
Expect to be asked about all aspects of your business, not just engineering. Good candidates will be interested in your business model, customers, office life, company history, and leadership. Questions about remuneration, benefits, and perks are less appropriate at this stage, but interviewees may clarify information you put in your job description.
After that, finishing up the phone screening is as simple as thanking the interviewee for their time and informing...