If you switch to a new phone, you can continue using the app by installing the "Hobonichi Techo App" on your new device and logging in with the same account.
Regarding the transfer of data recorded in the app, please refer to the following as it differs depending on your plan only for photos and videos.
*For instructions on how to switch devices when you switch to a new phone, please refer to this Help page.
On the Free Plan
About photo and video
With the Free Plan, photos and videos that have not been clipped to "Today's Cover" will not be transferred when you switch to a new device.
*On the Free Plan, any photos or videos other than those clipped to the "Today's Cover" are not uploaded to the cloud.
*Even if you transfer photo and video data from your old device to your new one, the app cannot recognize them as the same files because the device ID changes. Therefore, past photos and videos cannot be loaded or displayed on the app.
Reference: Differences between Free and Premium Plans for Photos and Videos (Help)
About other data
Data other than photos and videos, including records based on Location information, Schedule, Health, Notes, and Today’s Reflection, are all uploaded to the cloud even with the Free Plan, so the data will be transferred even if you switch devices.
On the Premium Plan (Paid)
About photo and video
With the Premium Plan, all photos and videos recorded after subscription are automatically uploaded to the cloud. Therefore, photos and videos uploaded to the cloud will be transferred even if you switch devices.
*Photos and videos that have not completed uploading to the cloud will not be transferred.
*Photos and videos recorded before subscribing to the Premium Plan are not automatically uploaded to the cloud.
Reference: How to check the upload status of photos/videos and how to upload them manually (Help)
About other data
Data other than photos and videos, including records based on Location information, Schedule, Health, Notes, and Today’s Reflection, are all uploaded to the cloud, so the data will be transferred even if you switch devices.