Safari memo keeps popping up on iPhone
You are (perhaps inadvertently) using Handoff between your iPhone and your Mac Mini. This Support Page at Apple describes the Handoff setup process.

Extracted from the Support Page:

Turn Handoff on or off

Note: If you don’t see a Handoff option on your device, it doesn’t work with Handoff.


On your Mac: Choose Apple menu > System Preferences, click General,
then select “Allow Handoff between this Mac and your iCloud devices”
(below “Recent items”). To turn it off, deselect the option.
On iPad, iPhone, or iPod touch: Go to Settings > General > Handoff,
then tap to turn on Handoff. To turn it off, tap the option.