It has already been stated that phalasamapatti (fruition attainment) first begins to occur when arising from nirodhasamapatti. This phalasamapatti being free from raga (passion), etc., it is also called suññata(the Void). As it is free of raga-nimitta (one of the attributes of sentient existence), it is also known as animitta. Moreover, as it is free from passionate desire such as raga, etc., it is also called appanihita. As such, phassa which is also included in this samapatti is also known as suññata, animitta and appanihita. As phassa (contact) takes place by dwelling upon Nibbana, which is known as suññata (the Void), animitta (the Unconditioned), and appanithta (freedom from longing or desire), with attentive consciousness of mind, it is called suññata, etc. The answer, therefore, is that the three kinds of phassa, viz: suññataphassa, animittaphassa and appanihitaphassa first begin to take place.
For better understanding, it may be stated that when arising from nirodhasamæpatti,contact takes place with suññata-nibbana, a condition devoid of kilesa-sankhara to which the mind has been directed as its sense-object. Contact is also made with animitta-nibbana which is devoid of or free from any sign of nimitta. Then comes mere awareness of contact with appanihita-nibbana, a condition free from vehement desire, which is the sense object that has been contemplated.
http://www.dhammaweb.net/mahasi/book/Mahasi_Sayadaw_Culavedalla_Sutta.pdf