Phrasentext statt Instanz von class \XF\Phrase

[Admin]

Kirby: A XenForo phrase created in PHP code is an instance of class \XF\Phrase.

If you want it's string representation, you can just cast it to a string (as the class implements __toString magic method):

$upgradeDescription[$userUpgradeId]['description'] = (string)\XF::phrase($descriptionPhrase);