The most direct and appropriate method to meet the requirement is to place the contact information inside a Block element and enable its "Collapsible" property. The Block element acts as a container for other elements on the FlexCard. By setting its Collapsible property to true, the platform automatically adds a control (e.g., a chevron icon and label) that allows the end-user to expand and collapse the block's content on demand. This precisely fulfills the requirement for the contact information to be visible only as needed by the user, while the account information remains static.

1. Salesforce OmniStudio Documentation

FlexCard Designer: The official documentation details the properties of FlexCard elements. The "Block" element is described as a container that has a "Collapsible" checkbox property. When selected

the block can be collapsed and expanded by the user. This is the standard

built-in feature for this use case. (Reference: OmniStudio Developer Guide

Section: "FlexCard Element Reference"

Subsection: "Block Element Properties").

2. Salesforce Trailhead

OmniStudio FlexCards: The "Build a FlexCard" module demonstrates the use of various elements. It shows that to group elements and make them collapsible

you should use a Block element and check the "Collapsible" property in the properties pane. (Reference: Trailhead

Module: "OmniStudio FlexCards"

Unit: "Add and Configure Elements on a FlexCard").