public RequestCollection<IRequest> Source
    {
        set
        {
            repeater.DataSource = value;
            repeater.DataBind();
        }
    }

protected void rList_DataBound(object source, RepeaterItemEventArgs e)
    {
        if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem)
        {
            LinkButton phone = e.Item.FindControl("lbPhone") as LinkButton;
            Label client = e.Item.FindControl("lClient") as Label;
            Label created = e.Item.FindControl("lCreated") as Label;
            //....

            if (e.Item.DataItem is Class1)
            {
                Class1 class = e.Item.DataItem as Class1;
                phone.Text = class.Phone;
                phone.CommandArgument = class.Id.ToString();
                //....
                
            }
            if (e.Item.DataItem is Class2)
            {
                Class2 class2 = e.Item.DataItem as Class2;
                phone.Text = class2.Phone;
                phone.CommandArgument = class2.Id.ToString();
                //....
            }
        }
    }

var item = подобрать нужный класс
phone.Text = item.Phone;
phone.CommandArgument = item.Id.ToString();

class Base
{
string Phone {get; set;}
string Client {get; set;}
//...
}

class Class1 : Base, IRequest
{
// поля класса
}

class Class2 : Base, IRequest
{
// поля класса
}

interface IRequest
{
// поля базового класса + некоторые поля общие для Class1, Class2 ....
}