The phone will be known as the Librem 5 and will use Plasma Mobile, a version of the KDE software that is available for use on Linux desktops.
The Foundation said it would create hackfests, tools, and emulators, and also build awareness in order to move GNOME/GTK on to the Librem 5 phone.
“Having a Free/Libre and Open Source software stack on a mobile device is a dream come true for so many people, and Purism has the proven team to make this happen," said Neil McGovern, executive director of the Foundation.
"We are very pleased to see Purism and the Librem 5 hardware be built to support GNOME.”
Purism founder and chief executive Todd Weaver said his company was excited to work with many communities and organisations to advance the digital rights of people.
"Getting endorsement from the GNOME Foundation for the Librem 5 hardware gets us all one step closer to a phone that avoids the handcuffs of Android and iOS,” he added.