Phillips, who is departing at the end of May, is to be replaced by current Chief Operating Officer Craig Cook from the start of June.
Cook is also currently head of research & development, and he will be replaced in this role by current Senior Vice-President of Translational Medicine Steve Damment.
Non-Executive Chairman Rolf Stahel said: "I would like to thank Jim for his contribution over the last five years and wish him every success in his future endeavours. Under his dedicated leadership the company has transformed since 2013 from an academic entity to a publicly-funded, commercially-focused biotech company with strong prospects."
He added: "We are also fortunate that in Dr Cook we have an internal candidate who can take over responsibility as CEO, ensuring continuity and a controlled handover. Craig will provide strong leadership, demonstrated expertise, a deep understanding of the business, and a relentless focus on delivery of key value-driving programs to take Midatech into its next phase of growth. We have every confidence that Craig, together with his senior management team, will drive Midatech to a successful future."
Shares were up 1.6% on Thursday at