Unless explicitly stated otherwise by the event producer or event organizer, ticket QR codes (the square barcodes accessible from your ticket confirmation email) can generally be scanned at the event entry on your smartphone. When permitted, please ensure your device brightness is suitably high to allow scanning without issue (at least 50%).
Under normal circumstances you are not required to bring printed tickets. Depending on the event type, exceptions may exist. Examples such as conferences, where all attendees and delegates are often required to wear conference badges around their neck may require a printed ticket.