If people are complaining and are not showing will to share their private numbers with telegram because many people don't want to let others know about their relation with cryptos to avoid future complications. Why don't you allow them to proceed in simple way. This isn't excuse to use word extra security. Let people to decide what they want to share flexibly.
It's not just a phone number. Just look what permissions Telegram app requires:
Telegram
Telegram Messenger LLP
This app has access to:
Identity
find accounts on the device
add or remove accounts
read your own contact card
Contacts
find accounts on the device
read your contacts
modify your contacts
Location
approximate location (network-based)
precise location (GPS and network-based)
SMS
read your text messages (SMS or MMS)
receive text messages (SMS)
Phone
directly call phone numbers
read call log
read phone status and identity
write call log
Photos/Media/Files
read the contents of your USB storage
modify or delete the contents of your USB storage
Storage
read the contents of your USB storage
modify or delete the contents of your USB storage
Camera
take pictures and videos
Microphone
record audio
Wi-Fi connection information
view Wi-Fi connections
Device ID & call information
read phone status and identity
Other
receive data from Internet
view network connections
create accounts and set passwords
pair with Bluetooth devices
full network access
change your audio settings
read sync settings
run at startup
draw over other apps
control vibration
prevent device from sleeping
toggle sync on and off
install shortcuts
uninstall shortcuts
read Google service configuration
Updates to Telegram may automatically add additional capabilities within each group.