Globus said his decision follows "a change in personal circumstances" and will allow him to "focus on his wellbeing and plan for his next chapter".
Recruitment for Shipman's successor will start soon, said Globus, with Managing Director Lesley Taylor stepping in to support the group's UK and Ireland sales team until a replacement is found.
Shipman's travel industry CV includes spells at Classic Collection, Sani/Ikos Group, and G Touring brands Travelsphere and Just You.
Globus said Shipman had been "instrumental" in growing and strengthening the trade team across Cosmos Tours, Globus Journeys and Avalon Waterways.
In addition, Globus hailed the "pivotal role" Shipman played in the launch of Avalon Waterways and Cosmos Tours in the Irish market.
"UK and Ireland Managing Director of Globus Family of Brands, Lesley Taylor, and the whole team are very grateful for the leadership, dedication and camaraderie Phil has shown over the last three years," said the group.
"He will be much missed by everyone at the company both in the UK and globally across the USA and Australia. Phil is very well known within travel having worked in the industry for a remarkable 30 years. This pause will give Phil time to reflect and consider potential new avenues."