Many people often experience difficulties in achieving behavioral goals related to smartphone use. Most of prior studies approached this problem with various behavior change strategies such as self-reflection and social support. However, little is known about the effectiveness and user experiences of restrictive and coercive interventions such as blocking. In this work, we developed "GoalKeeper," a smartphone intervention app that locks the user into the self-defined daily use time limit with restrictive intervention mechanisms. We conducted a four-week field experiment with 36 participants to investigate the effects and user experiences of varying intensities of restrictive interventions. The results showed that restrictive mechanisms are more effective than non-restrictive mechanisms such as warning. However, we found that restrictive mechanisms caused more frustration and pressure to the users, mainly due to diversity of usage contexts and needs. Based on our study results, we extracted practical implications for designing restrictive mechanisms that balance the intervention effectiveness for behavioral changes and the flexibility for user acceptability.