Walker will start on three days' rest Sunday against the Cubs, Todd Zolecki of MLB.com reports.
The Phillies demoted struggling starting Bailey Falter and didn't call up anyone to replace him, so they'll need to get creative with the pitching. Walker will be available on short rest after getting knocked out in the first inning of his previous start Wednesday against the Giants. Walker has struggled in his first nine starts as a Phillie, posting a 6.53 ERA and 1.50 WHIP.