This is a keycap with the number 5 written on it. You can see the keycap on the keyboard
⌨️ or telephone dial pad
☎️. It has a similar meaning to
🖐 in gestures and can be used to represent the number 5. Other keycap emojis:
#️⃣*️⃣0️⃣1️⃣2️⃣3️⃣4️⃣6️⃣7️⃣8️⃣9️⃣🔟