It's pretty easy. First of all send to the view decoded variable (see Laravel Views):
view('your-view')->with('leads', json_decode($leads, true));
Then just use common blade constructions (see Laravel Templating):
@foreach($leads['member'] as $member)
Member ID: {{ $member['id'] }}
Firstname: {{ $member['firstName'] }}
Lastname: {{ $member['lastName'] }}
Phone: {{ $member['phoneNumber'] }}
Owner ID: {{ $member['owner']['id'] }}
Firstname: {{ $member['owner']['firstName'] }}
Lastname: {{ $member['owner']['lastName'] }}
@endforeach