A non-cash benefit (German: geldwerter Vorteil) is a benefit in kind that employers can grant employees on top of their regular pay. It can be a product, for example a discount on the company's own products, or a service.
Under German tax law, non-cash benefits generally have to be taxed. A company phone is an exception: since the law treats it as work equipment, it's tax-free — even when the device is also allowed for private use (a "COPE" setup).
Company phones and employment law (in German)
Company phone taxation for private and business use (in German)