There may be a setting that’s not quite right in your iPhone’s Outgoing Mail section. The username (email address), password and Host/Server Name (mail.webserverlink.com) need to be filled in (this applies to both the Incoming and Outgoing Mail sections).
You can find the Outgoing Mail Server settings page by following this path:
Settings > Mail > Accounts > *your account* > Account > Outgoing Mail Server SMTP mail.webserverlink.com > Primary Server mail.webserverlink.com