"work informally" is a correct and usable phrase in written English.
It can be used to describe an arrangement or relationship where rules and formalities are relaxed and tasks or activities may be handled without following a strict protocol. For example, "Our team decided to work informally to come up with a creative solution to the problem."
Students are asked to comment on the mood and theme of the work informally, through questions.
Many migrant domestic workers choose to work informally, despite their vulnerabilities, because they have worse problems at home.
This is largely because many of the residents work informally, and are therefore unable to secure the documents needed to rent outside the villas.
At the end they will be invited to show their work informally and receive feedback, but there is no requirement for a final performance or commission.
Depressingly few women work in formal jobs, but many work informally (pdf), in areas such as tailoring, ghee manufacturing and leather craftwork.
But then, fooling with her sister's Rolleiflex, she turned to camera work, informally studying with no less a mentor than Andre Kertesz.
Robert K. Wittman, a former F.B.I. agent who ran the agency's art-crime team, said that he has been working informally on behalf of several museums Mr. Landis visited to gather more information about his actions, with the aim of determining whether a legal case could be built against him for theft of goods and services.
For some years now, I've worked informally for the Ministry of State Security.
Last fall during the lockout, Lundqvist worked informally with the elder Lehner to stay fresh.
By the time he was in his teens, he was working informally with a drummer named Ray White.
In his later years, he was a consultant and worked informally to improve the United States' relations with China and Indonesia.
