Hi @Kilkent,
Well, please see the following Quotes:
"
Microsoft Flow is a fully public cloud service, and everyone in the world can sign up and use it to automate their day-to-day tasks. To use Microsoft Flow there is no requirements that users have or use an Office 365 account. Because of this, there’s no mechanism at this time for you to block another person from using Flow (as everyone in the world can, irrespective of their email address).
However, if a person signs up for Microsoft Flow, and you choose to not support them inside of your organization, they can in no way incur costs to your company. When an individual signs up for Microsoft Flow, that is a relationship between that individual and Microsoft directly, like any many public cloud services from Microsoft, such as Bing, Wunderlist, OneDrive or Outlook.com, and does not in any way imply that the service is provided by your organization.
Finally, if your company wishes to restrict the use of organizational-only data inside of Microsoft Flow, that is possible through Data loss prevention (DLP) policies.
"
Please read more in the article below:
Flow in your organization Q&A
If you have any further questions, please feel free to post back.
Regards