Lemlist isn't really built for enrichment — it's primarily an outbound email tool. While they do have some basic enrichment features, you're going to hit limitations pretty quickly if data quality is important to your campaigns.
For phone number finding specifically, Lemlist partners with a few data providers but their coverage and accuracy isn't great compared to dedicated enrichment tools. You'll get maybe 20-30% phone number coverage on a typical B2B list.
Most practitioners I know run their enrichment outside of Lemlist first, then import the enriched data. The standard waterfall setup is usually Clay → Apollo/ZoomInfo → LeadMagic for verification, then push clean data into Lemlist for the actual outreach.
If you're dead set on doing it within Lemlist, you can use their "Enrich" feature in the campaign builder, but expect to pay their markup on data credits plus deal with lower match rates. Their phone data comes through partners like Dropcontact, which is decent for European numbers but spotty for US coverage.
Honestly, you'll save money and get better results building a proper enrichment stack upstream. Clay gives you way more flexibility with multiple data sources, and you can verify everything with LeadMagic before it hits your sender reputation in Lemlist. The extra setup time is worth it for the data quality improvement.