Not straight forward but we can add company name from the following file -
~/CMSModules/ContactManagement/Pages/Tools/Contact/List.aspx
<cms:UniGrid runat="server" ID="gridElem" ObjectType="om.contact" OrderBy="ContactLastName"
Columns="ContactID,ContactLastName,ContactFirstName,ContactEmail,ContactCompanyName,ContactStatusID,ContactCountryID,ContactCreated"
IsLiveSite="false" HideFilterButton="true" RememberDefaultState="true" RememberStateByParam="" FilterLimit="0">
<GridActions Parameters="ContactID">
<ug:Action Name="edit" Caption="$om.contact.list.manage$" FontIconClass="icon-eye" FontIconStyle="Allow" />
<ug:Action ExternalSourceName="delete" Name="delete" Caption="$General.Delete$" FontIconClass="icon-bin" FontIconStyle="Critical"
ModuleName="CMS.ContactManagement" Permissions="Modify" />
</GridActions>
<GridColumns>
<ug:Column Source="ContactFirstName" Caption="$om.contact.firstname$" Wrap="false" />
<ug:Column Source="ContactLastName" Caption="$om.contact.lastname$" Wrap="false" />
<ug:Column Source="ContactEmail" Caption="$general.emailaddress$" Wrap="false" />
<ug:Column Source="ContactCompanyName" Caption="Contact Company Name" Wrap="false" />
<ug:Column Name="ContactStatusID" Source="ContactStatusID" ExternalSourceName="#transform: om.contactstatus.contactstatusdisplayname" AllowSorting="false" Caption="$om.contactstatus$" Wrap="false" />
<ug:Column Name="ContactCountryID" Source="ContactCountryID" ExternalSourceName="#transform: cms.country.countrydisplayname" AllowSorting="false" Caption="$general.country$" Wrap="false" />
<ug:Column Source="ContactCreated" Caption="$general.created$" Wrap="false" />
<ug:Column Source="ContactGUID" Visible="false" />
<ug:Column CssClass="filling-column" />
</GridColumns>
<GridOptions DisplayFilter="true" ShowSelection="true" FilterPath="~/CMSModules/ContactManagement/Controls/UI/Contact/Filter.ascx" />
</cms:UniGrid>
CompanyName is a default field on Contact class.
Note: We need to manually check this code after any upgradation done in future because this change is done by manually and changed default behavior of contact list functionality.