A phone system that works fine for five employees can fall apart at twenty five, not because the technology fails, but because it wasn't built to scale in the first place.
The businesses that avoid this pain plan ahead. Cloud based systems let you add users, lines, and locations without new hardware or a lengthy install. Look for a setup where growth means a quick account change, not a multi week project with a technician on site.
If you're planning to add staff, open a new location, or bring on seasonal workers this year, it's worth checking now whether your current system can actually handle it, before you're scrambling mid growth spurt.