If they didn't give you the email information, I don't see how you can find it using their phone number. They might not have an email address or it is more likely that they might have several. You can send them a phone text message. You would need to find out what phone carrier they use and each carrier has a way to send messages to their customer phones. They usually have an SMS gateway and an MMS gateway. MMS has more capability.
Sending text message from PC
1) get their phone service provider at carrierlookup.com ( Phone# => T-mobile => SMS gateway: tmomail.net
OR use http://freesmsgateway.info/ to look up SMS gateway
(can get a free SW at
https://github.com/typpo/textbelt )
2) email to nnnnnnnnn.ccccc (n=phone#; c=carrier SMS gateway)
keep text under 160 characters.
Carrier SMS gateway domain MMS gateway domain
Alltel [insert 10-digit number]@message.alltel.com [insert 10-digit number]@mms.alltelwireless.com
AT&T [insert 10-digit number]@txt.att.net [insert 10-digit number]@mms.att.net
Boost Mobile [insert 10-digit number]@myboostmobile.com [insert 10-digit number]@myboostmobile.com
Cricket Wireless [insert 10-digit number]@sms.cricketwireless.net [insert 10-digit number]@mms.cricketwireless.net
Project Fi [insert 10-digit number]@msg.fi.google.com [insert 10-digit number]@msg.fi.google.com
Sprint [insert 10-digit number]@messaging.sprintpcs.com [insert 10-digit number]@pm.sprint.com
T-Mobile [insert 10-digit number]@tmomail.net [insert 10-digit number]@tmomail.net
U.S. Cellular [insert 10-digit number]@email.uscc.net [insert 10-digit number]@mms.uscc.net
Verizon [insert 10-digit number]@vtext.com [insert 10-digit number]@vzwpix.com
Virgin Mobile [insert 10-digit number]@vmobl.com [insert 10-digit number]@vmpix.com
Republic Wireless [insert 10-digital number]@text.republicwireless.com
see
https://en.wikipedia.org/wiki/SMS_gateway for the full list