Broaden out
Definition 1 of 2
Pro Tip 1/3Inclusiveness
Use 'broaden out' to suggest including more people or ideas. 
We need to broaden out our club membership to attract diverse individuals.
Pro Tip 2/3Physical Expansion
Applies to physical space becoming larger or wider. 
The road broadens out after the bridge to accommodate more traffic.
Pro Tip 3/3Not Literal
'Broaden out' is often used metaphorically, not describing physical size. 
The discussion broadened out to include ethical concerns.