I fixed your SQL Injection problem too.... You may have to adjust syntax as my IDE's are all occupied so I'm writing this direct
StringBuilder sb = new Stringbuilder("SELECT ");
sb.AppendLine("NameCount = (SELECT Count(1) FROM tblContact WHERE FullName = @FullName)");
sb.AppendLine(", PhoneCount = (SELECT Count(1) FROM tblContact WHERE Phone = @Phone)");
sb.AppendLine(", EmailCount = (SELECT Count(1) FROM tblContact WHERE Email = @Email)");
string strSQL = sb.ToString();
SqlCommand cmd = new SqlCommand(strSql, "connection");
cmd.Parameters.AddWithValue("@FullName", txtFullname.Text);
cmd.Parameters.AddWithValue("@Phone", txtPhone.Text);
cmd.Parameters.AddWithValue("@Email", txtemail.Text);